The present embodiments relate generally to ion optical elements that may be used, for example, in time-of-flight mass spectrometers, ion mobility spectrometers, ion guides, collision cells, reaction cells or other instruments.
Time-of-flight mass spectrometers (TOFs) can be used to separate ions and determine their mass-to-charge ratios. In a linear TOF, ions are rapidly accelerated through a potential difference to a set kinetic energy and then travel in a straight line down a flight tube. The arrival of the ions at the far end of the flight tube is detected, typically with a microchannel plate or a very fast electron multiplier. If different ions have different masses, the lighter ions travel faster and arrive at the detector sooner. The difference in time-of-arrival may be used as a measure of the mass-to-charge ratio (m/z) of the ions. TOF mass spectrometers are described in, for example, U.S. Pat. Nos. 7,154,086 and 8,084,732 which are incorporated herein in their entireties.
Ion mobility spectrometers (IMS) may also be used to separate and identify analyte ions. Unlike time-of-flight mass spectrometers, which operate in a high vacuum such that collisions with background gas can be neglected, ion mobility devices operate at atmospheric pressure or at vacuum levels poor enough that analyte ions are constantly losing kinetic energy through collisions with the background gas. Because the size, shape and mass of an analyte ion affects its mobility, ion mobility spectrometers measure the transit time for an ion to travel a set distance. Since the motion of an ion is constantly damped, the ions are typically subjected to an electric field as they travel through the IMS. An IMS typically comprises a series of equally-spaced rings with an equal voltage drop between each pair of rings. Such a device is depicted FIGS. 1 and 2 in U.S. Pat. No. 7,081,618, which is incorporated by reference herein in its entirety.
Ion guides, collision cells and reaction cells may be used as components in mass spectrometers. Ion guides may be used as a component in TOF or quadrupole mass spectrometers to transport ions through different stages of the mass spectrometer system. An example of an ion guide is described in U.S. Pat. No. 6,812,453 which is incorporated by reference herein in its entirety.
Collision cells may be used to fragment ions in a sample in order to determine their structure or to achieve more sensitive or more specific analyses. A simple collision cell is described in U.S. Pat. No. 4,234,791, which is incorporated by reference herein in its entirety. In a collision cell, radio frequency (RF) fields are used to confine ions radially as they travel through a quadrupole, hexapole or other multipole ion guide. The gas pressure inside the ion guide is raised and ions are injected into the ion guide with enough energy to cause fragmentation of the ions when they collide with the neutral gas molecules inside the collision cell. These ion fragments can then be analyzed by a mass analyzer. In many cases, it has been found useful to provide an axial electric field to keep ions moving through and out of the collision cell. Various means for providing such an axial field are described in U.S. Pat. No. 5,847,386, which is also incorporated by reference in its entirety herein.
Reaction cells are generally structurally similar to collision cells, but use a reaction gas such as ammonia, methane, oxygen or hydrogen (or mixtures of reaction gases) that react with the sample to reduce or eliminate isobaric interferences.